You don't wear a graduation cap when visiting a graduation party. No onesie to a baby-shower, nor a tie with houses on it for a house warming party. Neither do we all love those red and green Christmas sweaters that get trotted out to Christmas parties.
When we Dutch folks, and even Europeans in general, bring food to a party, the whole focus is on "breaking bread together". The reason we eat with people is to get to enjoy each others company. Sharing food accomplishes this more than anything else. North Americans seem to get hung up on the theme of the celebration. On birthday cakes we see fake, sometimes even non-edible, items to highlight the theme, instead of focusing our attention on the people we are celebrating with. We get served food that has sacrificed flavor for looks. So we will see a fondant diaper on a baby-shower cake, spiders on Halloween cakes, and most nearly every other non edible, unnaturally coloured decor on their cakes.
When asked at the bakery if we make birthday cakes, I'm often confused, although I understand the question. Yes, we make cakes! Of course you may eat them at a birthday party; you can eat them anytime! We are easy going like that. We believe food should be pleasing to both the eye and the palate. We really enjoy being able to create a beautiful cake using all the natural beauty that God has placed around us in the wide array of colours and shapes in fruit, nuts, chocolate, etc. So you can ooh and aah over the cake and then turn your focus back to the most important part of the celebration: enjoying time with your family and friends--even those who showed up in Christmas sweaters!